1. Field of the Invention
The present invention relates to an apparatus for manufacturing a container including a barrel with an open end thereof closed by a cover having a peripheral edge fastened to the peripheral edge of the barrel open end, the barrel having a necked-in portion.
2. Description of Background Art
One general metallic container includes a barrel of metal having an open end thereof closed by a cover of metal having a peripheral edge thereof fastened to the peripheral edge of the open end of the barrel to form a double seam. The barrel is necked in to provide a necked-in portion adjacent to the double seam.
Japanese Laid-Open Patent Publication No. 58-35027 discloses a method of making such a container with a conventional apparatus by fastening a container barrel and a cover together into a double seam and simultaneously necking in the container barrel. The disclosed method is shown in FIGS. 10 and 11(A) through 11(C). As shown in FIG. 11(A), a metallic container cover b includes a chuck wall c having an outside diameter smaller than the inside diameter of an open end of a metallic container barrel a. First, the chuck wall c is fitted in the open end of the barrel a. A rotatable seaming chuck d with its diameter equal to the inside diameter of the chuck wall c is mounted on the cover b with the outer side wall of the seaming chuck d being held against the inner surface of the chuck wall c. Then, as illustrated in FIGS. 10 and 11(B), a first seaming roll e is pressed against the barrel a and the chuck wall c toward the seaming chuck d for preliminarily fastening a flange i of the barrel a and an end hook h of the cover b. At the same time, the barrel a is preliminarily necked in by a shoulder or jaw f of the first seaming roll e, thus forming a necked-in portion j. Thereafter, a second seaming roll g is pressed against the preliminarily fastened end hook h and the flange i to fasten them to each other while deforming them toward the chuck wall c, thereby perfecting the necked-in portion j and providing a double seam k.
In the above method, it is important that the first seaming roll e and the second seaming roll g be moved toward the seaming chuck d for accurately selected distances and under exactly adjusted pressures when the barrel a and the cover b are fastened together. In recent years, the barrel a and the cover b are made of a highly hard material such as tin-free sheet steel and fastened to each other at high speed. Unless the distances and pressures were well selected and adjusted for the rolls e, g, the necked-in portion j would have wrinkles 1 as shown in FIG. 10 at X, the double seam k would not sufficiently be fastened, and the necked-in portion j would have an irregular outer shape. More specifically, the cover b as it is rotated during the fastening process is subjected to high resistance against forced deformation thereof, and the roll e or g and the cover b are pressed against each other through an extremely small area. Therefore, if the distance of movement of the roll e or g or the pressure applied thereto were varied, the necked-in portion j would tend to produce the wrinkles 1 as illustrated in FIG. 10, or the roll e or g and the cover b might slip with respect to each other. As a result, the barrel a and the cover b would not be well fastened together in the double seam k. The irregular profile of the necked-in portion j would result in an impaired appearance of the produced container. The rolls e and g would be apt to undergo rapid wear because of the slippage during the fastening process, and could not be used for a long period of time.